Download Dual Input All-Pass Networks Using MO-OTA and its Application

Dual Input All-Pass Networks Using MO-OTA
and its Application
Pipat Prommee1, Krit Angkeaw2, Jirasak Chanwutitum2, and Kobchai Dejhan1
Faculty of Engineering and Research Center for Communication and Information Technology
King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand
Tel: +66-2326-4238, +66-2326-4242, Fax: +66-2326-4554
2
Industrial Electrical Technology Department, Faculty of Engineering
King Mongkut’s Institute of Technology North Bangkok, Bangkok 10800, Thailand
Email: [email protected]
1
Abstract— This paper presents a realization of grounded passive
elements first order all-pass networks using a multiple-output
operational transconductance amplifier (MO-OTA) and three
grounded passive elements. The proposed circuit is operated in
current-mode for the good benefit as well as high output
impedance and cascadability. Therefore, it can be directly
employed as a subsystem of monolithic circuit without additional
matching circuits. Furthermore, a new quadrature oscillator is
presented as an application for confirmed the theory and realistic
practically. The PSpice simulation results verifying of theoretical
are also included.
I. INTRODUCTION
Current mode signal processing circuits have recently
demonstrated many advantages over their voltage mode
counterparts including increased bandwidth, higher dynamic
range and better suitability for operation in reduced supply
environment [1]. In many papers, current mode circuits are
presented by using CCII based [2]-[4]. Unfortunately, CCII
does not have a differential input. The OTA is a familiar
device for voltage-mode and current-mode applications. The
OTA provides a highly linear electronic tunability and a wide
frequency range. Moreover, OTA-based circuits require no
resistors and therefore, are suitable for monolithic
implementation and small die area [5]-[6]. The MO-OTA has
been proposed in previous paper [7]. From the strong points,
due to many output of OTA, the MO-OTA has more flexible
to use in term of a modern analog signal processing as well.
The previously presented all-pass filter topologies
employing conventional OPAMP [8-9] that ensure the low
bandwidth and voltage-mode are achieved. The FTFN [10],
Current Differencing Buffer Amplifier (CDBA) [11] and CCII
[2]-[4] are also introduced but some of these reports suffer
from floating passive components. The floating components
are trade-off in the practical realizations, parasitic
capacitances, bandwidth restrictions, complicated adjustment.
The floating node passive devices have to avoid in the design
for minimized the error reasons.
This paper presents the design of all grounded passive
elements all-pass network using one MO-OTA and three
grounded passive elements. The presented topologies can be
designed by using both in CMOS or bipolar technology. The
circuits comprise phase lead and phase lag Moreover, current
gain can be adjust by a transconductance (gm) through Iabc.
The simple construction and low voltage are proposed that
suitable for further IC fabrication.
II. THEORY AND PRINCIPLE
The OTA is a simple device that has been found in many
recently reports. The benefit of OTA is a voltage and current
mode realization can be done with a simple structure. The
tunable characteristic is a strong excellent point for the future
applications. The single output OTA is a conventional device
that might be has some restrictions on the design. The
modification of OTA can be eliminated that restrictions by
extended the output port namely a multiple-output OTA (MOOTA).
A. Multiple-output operational transconductance amplifier
The OTA has input as voltage and current output. The
simple structure of the well-known OTA, having used only
four transistors and current source. Figure 1 shows the symbol
of MO-OTA. The output current of MO-OTA yields
I o # " g m (V! V )
(1)
The transconductance gm is variable by bias current Iabc.
Note that the transconductance base on CMOS and bipolar
technology are equal to ($Iabc/4)1/2 and Iabc/2VT respectively. A
possible implementation of OTA using multiple output
operation transconductance amplifiers was proposed [12].
-Io
-Io
V-
V+
+Io
+Io
Iabc
Iabc
Io
V+
gm
V-
Fig.1. (a) CMOS MO-OTA structure and (b) symbol
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-Io
The transconductance of above CMOS OTA can be
expressed as:
gm #
$I abc
4
#
%COX WI abc
(2)
4L
The realization of the proposed all-pass network filter
using OTA is show in Fig.2. The circuit comprises one MOOTA, 2 grounded resistors and a grounded capacitor. From
this point of view, the proposed structure is simpler than the
other existing all-pass realizations [2]-[4]. In Fig.2(a) and
Fig.2(b), the all-pass transfer functions are realized as eq.3 and
eq.4 respectively.
The circuit model of a non-ideal OTA operating in
saturation region is shown in figure 3, where Ci is the input
capacitance, CO is the output capacitance and GO is the output
conductance. Generally GO is less than gm. The proposed
circuits in figure 2(a) and 2(b) can be express in term of high
frequency as eq(8) and eq(9), respectively.
Io
V+
Ci
gm(V+-V-)
Co
Go
-Io
VI1
0.5R
R
C
+I2
gm
I1
+I2
I1
-I2
I1
C
0.5R
(a)
(b)
Fig.2. Proposed Allpass Filter Networks
I2
+ sCR 1 (
# "K)
&
I1
* sCR ! 1 '
I2
+ 1 sCR (
# "K)
&
I1
* 1 ! sCR '
(3)
Go
gm R
2
1
RC
Fig.3. Circuit model for non-ideal case of the MO-OTA
+
sR.C ! 2Ci / 1 (
I2
&&
# " K ))
I1
* .sRC ! 1/.0.5sRCi ! 1/ '
(8)
+ 1 ! sR.C ! 2Ci / (
I2
&&
# " K ))
I1
* .1 ! sRC /.1 ! 0.5sRCi / '
(9)
(4)
(5)
III. QUADRATURE OSCILLATOR APPLICATION
The quadrature oscillator based on all-pass network is
shown in Fig. 4. The circuit consists of phase-lead and phaselag all-pass network configurations in Figs. 2(a) and (b). In
Fig. 4, the circuit can be oscillated due to the loop-gain is
unity, the transfer function can be expressed as
From Eq.(3), the phase shift are varying between 180, to
0, while (4), the phase shift are varying between 0, to -180,.
The pole frequency (-o) can be expressed as
-o #
Co
From (8)-(9) imply that the parasitic capacitances affect to
the poles and zeros of the transfer function at the high
frequency.
Gain (K) is a constant and defined as
K#
gm(V+-V-)
gm
-I2
R
Ci
+ 1 sC2 R2 (+ sC1R1 1 (
&&))
&& # 1
T1 ( s )T2 ( s ) # K1K 2 ))
* 1 ! sC2 R2 '* sC1R1 ! 1 '
(10)
(6)
Where the constants are K1=gm1R1/2 and K2=gm2R2/2,
loop-gain is unity independent with the any transconductances
, gmi. The phase of first all-pass network is written as
The passive sensitivities can be obtained as
S R-O # SC-O # 1
(7)
In Fig. 2, it can see that the output impedance of the
circuit is very high due to the OTA current output; hence it
can be directly interconnection with load or any current mode
circuits without the buffer circuit. The output current gain can
be adjusted by gm through the bias current Iabc.
1 (- ) # 2 tan 1 (-01 ) , 0 1 # C1R1
(11)
Likewise, the phase of second all-pass network is
1 (- ) # 180 2 tan 1 (-0 2 ) , 0 2 # C2 R2
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(12)
TABLE 1. PARAMETER USED IN SIMULATION
The frequency of oscillation can be given as
-#
-#
or
R1
C1
1
0 10 2
1
0.5R2
(OTA)2
gm2
Iout1
R2
0.5R1
(13b)
C1C 2 R1 R2
(OTA)1
gm1
(13a)
Iout2
.MODEL NMOS LEVEL=3 UO=460.5 TOX=1.0E-8 TPG=1
VTO=+0.62 JS=1.08E-6 XJ=0.15U RS=417 RSH=2.73
LD=0.04U VMAX=130E3 NSUB=1.71E17 PB=0.761 ETA=0.00
THETA=0.129
PHI=0.905
GAMMA=0.69
KAPPA=0.10
CJ=76.4E-5
MJ=0.357
CJSW=5.68E-10
MJSW=0.302
CGSO=1.38E-10
CGDO=1.38E-10
CGBO=3.45E-10
KF=3.07E-28 AF=1 WD=+0.11U DELTA=+0.42 NFS=1.2E11
DELL=0U LIS=2 ISTMP=10 TT=0.1E-9
.MODEL PMOS LEVEL=3 UO=100 TOX=1.0E-8 TPG=1 VTO=0.58 JS=0.38E-6 XJ=0.10U RS=886 RSH=1.81 LD=0.03U
VMAX=113E3
NSUB=2.08E17
PB=0.911
ETA=00
THETA=0.120 PHI=0.905 GAMMA=0.76 KAPPA=2 CJ=85E-5
MJ=0.429 CJSW=4.67E-10 MJSW=0.631 CGSO=1.38E-10
CGDO=1.38E-10
CGBO=3.45E-10
KF=1.08E-29
AF=1
WD=+0.14U DELTA=0.81 NFS=0.52E11 DELL=0U LIS=2
ISTMP=10 TT=0.1E-9
C2
Phase (deg) Gain (dB)
Fig. 4. The quadrature oscillator using proposed all-pass networks
From (13), the oscillation frequency is depended on
passive elements, R1, R2, C1 and C2. The components are
defined identically as R1=R2=R and C1=C2=C. The oscillation
frequency is actually becomes
-#
1
(14)
CR
IV. SIMULATION RESULTS
In order to confirm the validity of the proposed circuits,
PSpice simulation was carried out. The parameters used in
simulation are 0.5µm CMOS model obtained through
MIETEC as listed in table 1. The W/L parameters of MOS
transistors are assumed of 20µm/1µm for NMOS and
60µm/1µm for PMOS. The supplied voltages are VDD = -VSS
= 1.5 V. The corner frequency of 15.9 kHz are obtained with
such passive elements setting as R=10k2 and C=10nF. The
simulation results are illustrated for the current transfer
function characteristic in Fig.6 (a) and Fig.6 (b). The
characteristics represent for the phase response of phase-lead
and phase-lag all-pass filter, respectively. It can be observed
that the circuits provide a bandwidth for a several MHz. From
Fig.6, the effective of parasitic capacitances at output of OTA
are taken in order to the high frequency according to eq. (8)
and (9).
The application of proposed all-pass networks is a
quadrature oscillator as shown in Fig.4. The simulation result
of proposed oscillator application has shown in Fig. 7. The 2
outputs can be obtained for a quadrature behavior. The phase
different is about 90, according with the theoretical. The
waveform of the quadrature oscillator are in the assuming
conditions, gm1=gm2=200µs, R1=R2=10k2 and C1=C2=0.01µF.
The oscillation frequency can be obtained ensure that are in
agreement with the above theoretical about 16 kHz.
gain
phase
Fig .6 (a) The phase response of filter topology in Fig.2(a)
Phase (deg) Gain (dB)
gain
phase
Fig .6(b) The phase response of filter topology in Fig.2(b)
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[10] M. Higashimura, “Current-mode allpass filter using FTFN with
grounded capacitor,” Electron. Lett., vol. 27, pp. 1182-1183, 1991.
[11] A. Toker, S. Ozoguz, O. Cicekoglu, and C. Acar, “Current-mode allpass filters using current differencing buffered amplifier and a new highQ bandpass filter configuration,” IEEE Trans. Circuits and Syst., II, vol.
47, pp. 949-954, 2000.
[12] C.-C. Hsu and W.-S. Feng, “Structural design of current-mode biquad
filters,” Int. J. Electron., vol. 88, pp. 41-51, 2001.
[13] Z. Wang, “2-MOSFET transistors with extremely low distortion for
output reaching supply voltage,” Electron. Lett., vol. 26, pp. 951-952,
1990.
Iout1
Iout2
Fig. 7. Output waveform of quadrature oscillator in Fig. 4
V. CONCLUSION
The dual input multiple-output OTA all-pass filter
topologies with all grounded passive elements are presented.
The phase-lead and phase-lag can be simply modification with
a few passive components changed. The proposed topologies
does not limit for the implementation in bipolar or CMOS
technology. The proposed circuits tried to use the MOS
transistors for OTA realization. The output current can be
applied to next circuit without the any matching devices. The
cascadable topology is a benefit of proposed current mode
schemes. The cascade of proposed both types can be obtained
a quadrature oscillator as an application. Due to the minimized
component, decreasing components can be done by the
electronic resistors [13] that implemented from only 2 MOS
transistors. The oscillator will used only 2 capacitors for the
passive elements. The filter and oscillator simulation results
are obtained a good agreement with the theories suitable for
further IC fabrication.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
REFERENCES
C. Toumazou, C. Lidgey, and D. G. Haigh, Analogue IC design: the
current mode approach, Peter peregrinus ltd., 1990.
M. Higashimura and Y. Fukui, “Realization of current mode all-pass
networks using a current conveyor,” IEEE Trans. Circuits and Syst., vol.
37, pp. 660-661, 1990.
A. M. Soliman, “Generation of current conveyor based all-pass filters
from op-amp based circuits,” IEEE Trans. Circuits and Syst., II, vol.
44, pp. 324-330, 1997.
O. Cicekoglu, H. Kuntman, and S. Berk, “All-pass using a single
current conveyor,” Int. J. Electron., vol. 86, pp. 947-955, 1999.
E. Sanchez-Sinencio, J. Ramirez-Angulo, B. Linares-Barranco, and A.
Rodriguez-Vazquez, “Operational transconductance amplifier-based
nonlinear function syntheses,” IEEE J. Solid-State Circuit, vol. 24, no. 6,
pp. 1576-1586, 1989.
A. Rodriguez-Vazquez, B. Linares-Barranco, J. L. Huertas, and E.
Sanchez-Sinencio “On the design of voltage-controlled sinusoidal
oscillators using OTAs,” IEEE Trans. Circuits and Syst., vol. 37, pp.
197-211, 1990.
J. Ramirez-Angulo, and E. Sanchez-Sinencio, “High-frequency
compensated current-mode ladder filter using multiple output OTAs,”
IEEE Trans. Circuits and Syst., II, vol. 49, pp. 581-586, 1994.
J. V. Vosper, “Synthesis of first-order active-R allpass networks and
their application in sinusoidal oscillator design,” Electron. Lett., vol. 27,
pp. 53-55, 1991.
R. Holzel, “A simple wide-band sine wave quadrature oscillator,” IEEE
Trans. Instrum. Meas., vol. 42, pp. 758-760, 1993.
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